In a typical bi-folding door installation to which the present invention pertains, one or more folding door panels are mounted for movement about a vertical pivot axis located adjacent a lateral jamb member of a door frame. The pivot axis is defined by top and bottom pivot pins projecting from respective to and bottom edges of the panel to engage adjacent pivot brackets. The top pivot bracket is generally secured in a downwardly open guide track and the bottom bracket is normally secured to an adjacent jamb member of the door frame and/or to an underlying support. Such pivot assemblies are designed to adjust the vertical alignment of the door panel's pivot axis as well as the vertical position of the panel within the door frame opening. These adjustments generally are accomplished by laterally adjusting the position of the bottom pivot relative to the door frame and by extending or retracting the pivot pin to vertically raise or lower the door panel.
While a wide variety of such bottom pivot assemblies have been developed, that described in U.S. Pat. No. 4,106,158 issued Aug. 15, 1978, generally exemplifies the present state of the art with respect to commercially available low cost pivot assemblies.
As taught in that patent, a bottom pivot pin having a cylindrical shank is threaded into an internally threaded sleeve mounted in the bottom end of a pivotally suspended door panel. Threaded adjustment of the pivot pin in the sleeve determines the vertical position of the door panel in the door frame. The lower end of the pivot pin is formed by an externally splined conical head portion adapted to non-rotatably engage serrations formed along opposite edges of an elongated slot formed in a floor engaging bottom jamb bracket. Raising the door vertically serves to disengage the conical head of the pivot pin from the serrations whereby lateral repositioning of the pin along the bracket's slotted opening may take place to adjust vertical alignment of the door's pivot axis while threaded adjustment of the pin adjusts the door's vertical position.
While the simplicity of this structure has met with general commercial acceptance, in operation the conical head of the pivot pin has a tendency to disengage from the serrations of the bottom jamb bracket slot under sometimes relatively violent or jarring impact forces accompanying door opening and closing movements. This tendency permits the door's pivot axis to shift laterally and at times to effect rotational threading movement of the pin relative to the door mounted sleeve thereby to alter the vertical adjusted position of the door panel. Such tendency toward loss or change in door adjustment has created a demand for a bottom pivot assembly having a more positive and secure pivot adjustment system capable of maintaining door alignment. It is to just such an improved pivot assembly that the present invention is directed.